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Temperature Converter: Celsius, Fahrenheit, Kelvin and Temperature Change

Type one number and pick °C, °F or K under Convert from. The converter shows it two ways at once: as a reading, in the Absolute temperature card, and as a temperature change, in the Temperature change card. Results update on every keystroke and are worked out on your device, so nothing is uploaded.

How to use the temperature converter

Type a number in Temperature. Negatives, decimals and a decimal comma (1,5 or 1.5) all work.
If your phone keypad has no minus key, press ± beside the field to switch between positive and negative.
Choose the starting scale under Convert from: °C, °F or K. It starts on °F for visitors in the US and a few other regions and °C elsewhere, and it remembers your last pick.
Read the other two scales in each card. Every row has a copy button.

Reading or change: which card do you need?

A reading is what a thermometer shows. A change is how far the temperature rose or fell. They convert differently, because Fahrenheit and Celsius start from different zero points.

You have	Use	Rule
Today is 20 °C	Absolute temperature	°F = °C × 9/5 + 32, so 68 °F
It rose by 20 °C	Temperature change	°F = °C × 1.8, so +36 °F

That is why 0 °C is 32 °F, while a change of 0 °C is a change of 0 °F, and a 10 °C change is 18 °F. The tool prints the same reminder under the cards.

Celsius, Fahrenheit and Kelvin formulas

From → to	Reading	Change
°C → °F	°C × 9/5 + 32	× 1.8
°F → °C	(°F − 32) × 5/9	÷ 1.8
°C → K	°C + 273.15	× 1 (same size)
K → °C	K − 273.15	× 1 (same size)
°F → K	(°F − 32) × 5/9 + 273.15	÷ 1.8
K → °F	(K − 273.15) × 9/5 + 32	× 1.8

Results are rounded to three decimals at most, so 0 °F reads as −17.778 °C and 255.372 K.

Below absolute zero

Nothing is colder than 0 K (−273.15 °C, −459.67 °F). Enter a reading below that and the Absolute temperature card says so instead of showing a figure. The Temperature change card keeps working, since a fall of any size is still a change.

Other unit conversions

For lengths, weights and volumes, use the Measurement Converter. For cups, tablespoons and grams in a recipe, use the Cooking Measurement Converter.

Frequently asked questions

How do I convert negative Celsius to Fahrenheit?

Use the same formula as for any other number: multiply by 9/5 and add 32. So -5 °C is 23 °F, and -40 °C is -40 °F, the one point where the two scales agree. In the converter, type the number and press ± if your phone keypad has no minus key.

What is the Celsius to Fahrenheit formula?

°F = °C × 9/5 + 32. Going back, °C = (°F − 32) × 5/9. For example, 20 °C is 68 °F and 100 °C is 212 °F. The converter applies these as you type and rounds to three decimals at most.

How do I convert Fahrenheit to Kelvin?

Convert to Celsius first, then add 273.15: K = (°F − 32) × 5/9 + 273.15. So 50 °F is 283.15 K and 0 °F is 255.372 K. Pick °F under Convert from and the Kelvin figure shows in the Absolute temperature card.

What is 0 Kelvin in Celsius and Fahrenheit?

0 K is absolute zero: −273.15 °C or −459.67 °F. Type 0 with K selected and the Absolute temperature card shows both.

Can temperature be negative in Kelvin?

As a reading, no. Nothing is colder than 0 K, so if you enter a value below it, the Absolute temperature card says it is below absolute zero. A temperature change is different: a fall of 5 K is a perfectly good change, and the Temperature change card still shows it.

How do I convert a temperature difference from Celsius to Fahrenheit?

Multiply the change by 1.8 and do not add 32. A 10 °C rise is an 18 °F rise, and a 20 °C change is 36 °F. A change in kelvin equals the same change in °C, and going from °F, divide by 1.8. The Temperature change card does this for whatever number you type.

Can a temperature change be negative?

Yes. A fall is a negative change, such as −5 °C, which is −9 °F. The Temperature change card shows a + or − sign on every row, so a rise and a fall are easy to tell apart.

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